In underground coal mines, stone dusting of exposed rock surfaces is used to prevent and suppress fires caused by the ignition of coal dust and methane gas produced during the mining process. Stone dusting involves coating the surfaces of the mine with a fine-ground limestone dust. The dust adheres to the walls of the mine and prevents propagation of fires along exposed surfaces of unmined coal in the mine. In the event of the ignition of coal dust and gas within the mine, the concussion of an explosion and fire will cause the loosely adhering dust to fall from the surfaces of the mine to produce a limestone dust-air suspension that suppresses the propagation of flame and stops the fire.
In traditional stone dusting, a loose, poorly cohesive, dusty inert material is applied to the surfaces of walls and ceiling of the mine. In the event of a coal dust explosion, that the material is easily suspended into the air of the mine by the concussion. The traditional process of stone dusting is generally dusty and wasteful. Working personnel in the ventilation area have to be evacuated while the stone dusting procedure is performed because of the excessive amount of, respirable dust produced in the air of the mine during the stone dust application. The evacuation reduces the amount of time the mine can operate. In traditional practice, dust is applied by xe2x80x9cflingersxe2x80x9d. With this method, a substantial portion of the dust does not adhere to the surfaces of the mine and typically falls to the floor becoming wet and therefore inactive, leaving only a limited amount of material remaining usefully positioned on the walls and ceiling.
Kritchevsky, U.S. Pat. No. 2,195,573 discloses a method of laying dust which comprises contacting it with an aqueous solution of a condensation product of alkylolamine and a higher organic acid substance, preferably the higher fatty acids. This results in absorption of the aqueous material by the dust particles to a relatively substantial depth, with the result that the dust is prevented from becoming airborne when the surface is agitated.
Burns et al., U.S. Pat. No. 4,316,811 discloses a dust suppressant composition comprising polyethylene oxide crystalline thermoplastic, water soluble polymer, and the balance water. The dust suppressant composition can be applied by a variety of methods, such as spraying, immersion, painting, slurry and rinsing.
Kittle, U.S. Pat. No. 4,561,905 discloses a method of suppressing coal dust comprising the steps of diluting with water an emulsion comprising water, a surfactant, and oil which exhibits a tacky characteristic when in the form of a film in the absence of water. This mixture which is in the form of an emulsion is diluted and foamed. The foam is then sprayed into a mass of coal.
Roe, U.S. Pat. Nos. 4,971,720 and 5,143,645 disclose a foam formed from a solution of demineralized make-down water and foaming agent, wherein the foam is contacted with solid materials to suppress process dust emissions.
What is needed in the industry is a method of dusting coal mine surfaces to prevent and suppress fires and explosions in underground coal mines without the detrimental side effect of wasteful excess airborne dust production.
The present invention utilizes the cohesive property of foamed material composed of a small amount of water, with a fine grained mineral dust such as that obtained from limestone, dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, or fine ground mine tailings, and mixtures thereof; suspended in a foam. Dry mineral dust is blended with foam to produce a mass of material that is highly vesicular but that is cohesive and fluid enough to be pumped and sprayed as a foamed mass against mine wall surfaces and ceilings. The foamed material is applied with a spraying device that allows the foamed mass to adhere to the surfaces. Because of the low density of the material, the material can be built up to any thickness suitable for the application.
A significant advantage of the present invention is that no excessive airborne dust is produced during application, thus eliminating the need to evacuate the personnel in the area during application. The process is much cleaner and far less wasteful than normal stone dusting. After application, the low water content of the material permits evaporation of the water in the foamed mass, resulting in a dry mass of fine, poorly cohesive, vesicular material that dusts readily and has similar properties to that of the dry dust used in traditional stone dusting practice.
In one embodiment, the present invention includes a foamed material comprising limestone dust, a foaming agent and water.
In another embodiment, the present invention includes a foamed material comprising dust of at least one material selected from the group consisting of dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings, and mixtures thereof; a foaming agent and water.
In another embodiment, the present invention includes a dry powder formulation comprising limestone dust, a dry powder foaming agent and an additive that promotes the production of gas upon contact with water.
In another embodiment, the present invention includes a dry powder formulation comprising dust of at least one material selected from the group consisting of dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings, and mixtures thereof; a dry powder foaming agent and an additive that promotes the production of gas upon contact with water.
In another embodiment, the present invention includes a method of dusting coal mine surfaces comprising the steps of: providing a foam mixture comprising a foaming agent and water; incorporating air into the foam mixture to produce a foam; combining the foam and limestone dust to form a foamed material; and applying the foamed material to a mine surface.
In another embodiment, the present invention includes a method of dusting coal mine surfaces comprising the steps of: providing a foam mixture comprising a foaming agent and water; incorporating air into the foam mixture to produce a foam; combining the foam and dust of at least one material selected from the group consisting of dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings, and mixtures thereof, to form a foamed material; and applying the foamed material to a mine surface.
In another embodiment, the present invention includes a method of dusting coal mine surfaces comprising: providing a dry powder formulation comprising limestone dust, dry powder foaming agent, and an additive that promotes the production of gas upon contact with water; mixing the dry powder formulation with water to generate a foamed material; and applying the foamed material to a mine surface.
In another embodiment, the present invention includes a method of dusting coal mine surfaces comprising: providing a dry powder formulation comprising dust of at least one material selected from the group consisting of dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings, and mixtures thereof; dry powder foaming agent; and, an additive that promotes the production of gas upon contact with water; mixing the dry powder formulation with water to generate a foamed material; and applying the foamed material to a mine surface.
In a further embodiment, the present invention includes a method of dusting coal mine surfaces comprising: providing a dry powder formulation comprising limestone dust, dry powder foaming agent, and an additive that promotes the production of gas upon contact with water; and, applying the dry powder formulation to a wet surface.
In a further embodiment, the present invention includes a method of dusting coal mine surfaces comprising: providing a dry powder formulation comprising dust of at least one material selected from the group consisting of dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings, and mixtures thereof; dry powder foaming agent; and, an additive that promotes the production of gas upon contact with water; and, applying the dry powder formulation to a wet surface.
In another embodiment, the present invention includes a method of dusting coal mine surfaces comprising the steps of: providing a foam mixture comprising a foaming agent and water; incorporating air into the foam mixture to produce a foam; combining the foam and a water-insoluble, noncombustible, fire suppressant dust, to form a foamed material; applying the foamed material to a mine surface.
In certain embodiments of the present invention, foaming agents suitable for use with the method of the present invention can be dry powder or liquid and may include alkanolamides, alkanolamines, alkylaryl sulfonates, polyethylene oxide-polypropylene oxide block copolymers, alkylphenol ethoxylates, carboxylates of fatty acids, ethoxylates of fatty acids, sulfonates of fatty acids, sulfates of fatty acids, sulfate esters of fatty alcohols, sulfate esters of fatty alcohol ethoxylates, for example laurel ether sulfates, fluorocarbon containing surfactants, olefin sulfonates, olefin sulfates, hydrolyzed proteins, and mixtures thereof. A preferred dry foaming agent is an alpha olefin sulfonate sold under the trademark BIO-TERGE(copyright) from Stepan, Inc., Northfield, Ill. A preferred liquid foaming agent is Rheocell(copyright) 30 from Master Builders Inc., Cleveland, Ohio.
When referring to a mine throughout this specification, it is also meant to include a stope.
The present invention provides a novel foamed material for prevention and suppression of fires in mines, as well as a method for forming the foamed material using foam and the dust of limestone, dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings (dust) and mixtures thereof. The present invention further provides a method of dusting mine surfaces to prevent and suppress fires and explosions by applying the foamed material with a spray device that allows the foamed material to adhere to mine surfaces.
One embodiment of the present invention is a method for spraying a mine surface with a foamed material comprising the dust of limestone, dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings, and mixtures thereof; foaming agent; and, water; the method comprising activating the foaming agent to form pregenerated foam; adding the pregenerated foam to the limestone dust in a mixer; conveying the mixture to a spray nozzle which can be accomplished by pumping or by pneumatic conveyance; and spraying the foamed material onto the mine surface, wherein the foamed material adheres to the mine surface of the mine and dehydrates or loses moisture to form a porous coating.
Foaming agents suitable for use with the method of the present invention can be dry powder or liquid and may include alkanolamides, alkanolamines, alkylaryl sulfonates, polyethylene oxide-polypropylene oxide block copolymers, alkylphenol ethoxylates, carboxylates of fatty acids, ethoxylates of fatty acids, sulfonates of fatty acids, sulfates of fatty acids, sulfate esters of fatty alcohols, sulfate esters of fatty alcohol ethoxylates, for example laurel ether sulfates, fluorocarbon containing surfactants, olefin sulfonates, olefin sulfates, hydrolyzed proteins, and mixtures thereof. A preferred dry foaming agent is an alpha olefin sulfonate powder sold under the trademark BIO-TERGE(copyright) from Stepan, Inc., Northfield, Ill. A preferred liquid foaming agent is Rheocell(copyright) 30 from Master Builders Inc., Cleveland, Ohio. The dilution ratio of water to foaming agent may generally be about 20:1 (about 4.76% foaming agent in water) to about 60:1 (about 1.64%) but is preferably about 25:1 (about 3.8%) to about 35:1 (about 2.8%). Dilution ratios are a function of the composition of the foaming agent and are dictated by the typical use, and end use characteristics, of the foamed dust. Thus, the dilution rates of water to foaming agent may be considerably greater than those stated above; (for example, the dilution ratio of water to particular foaming agents may be in the thousands).
Alkanolamide foaming agents according to the present invention include, but are not limited to, those having from about 12 to about 20 carbon atoms
Alkanolamine foaming agents according to the present invention include, but are not limited to, those having from about 12 to about 20 carbon atoms.
Alkylaryl sulfonate foaming agents according to the present invention include, but are not limited to, those having one aryl group and having alkyl groups with about 12 to about 20 carbon atoms.
Polyethylene oxide-polypropylene oxide block copolymer foaming agents according to the present invention include, but are not limited to, those having about 10 to about 20 units of each block.
Alkylphenol ethoxylate foaming agents according to the present invention include, but are not limited to, those having an alkyl group of about 12 to about 20 carbon atoms.
Carboxylates of fatty acid foaming agents according to the present invention include, but are not limited to, those in which the fatty acid moiety has about 12 to about 20 carbon atoms.
Ethoxylates of fatty acid foaming agents according to the present invention include, but are not limited to, those in which the number of ethoxylate groups is about 10 to about 20 and the fatty acid moiety has about 12 to 20 carbon atoms.
Sulfonates of fatty acid foaming agents according to the present invention include, but are not limited to, those in which the fatty acid moiety has about 12 to about 20 carbon atoms.
Sulfates of fatty acid foaming agents according to the present invention include, but are not limited to, those in which the fatty acid moiety has about 12 to about 20 carbon atoms.
Sulfate esters of fatty alcohol foaming agents according to the present invention include, but are not limited to, those in which the fatty alcohol moiety has about 12 to about 20 carbon atoms.
Sulfate esters of fatty alcohol ethoxylate foaming agents according to the present invention include, but are not limited to, those in which the number of ethoxylate groups is about 10 to about 20 and the fatty alcohol moiety has about 12 to about 20 carbon atoms.
Fluorocarbon containing surfactant foaming agents according to the present invention include, but are not limited to, those having about 12 to about 20 carbon atoms and one or more CH2 moieties are replaced by CF2 moieties.
Olefin sulfonate foaming agents according to the present invention include, but are not limited to, those having about 12 to about 20 carbon atoms. Preferably, the olefin sulfonate used in the present invention is alpha olefin sulfonate.
Olefin sulfate foaming agents according to the present invention include, but are not limited to, those having about 12 to about 20 carbon atoms.
Hydrolyzed protein foaming agents according to the present invention include, but are not limited to, the derivatized products of the hydrolysis of proteins. The relative molecular weight of the protein can be any molecular weight that provides for foaming action in a cementitious mixture. Preferably, the relative molecular weight ranges from about 10,000 to about 50,000. Preferred hydrolyzed proteins are hydrolyzed gelatin, hydrolyzed collagen, and hydrolyzed proteins derived from blood. As an example but not a limitation of hydrolyzed gelatin is TG222 from Milligan and Higgins (Johnstown, N.Y.).
Other materials (including minerals) may be substituted for limestone as the dust component of the invention and, may include fillers or replacements for limestone. Examples, but not limitations of the materials that could be used for the dust incorporated in this invention are dolomite, magnesite, marble, Class F fly ash silica fume, gypsum, anhydrite, non-swelling clays, mine tailings and mixtures thereof. These materials or minerals are preferably water-insoluble, noncombustible, and may include organic or inorganic salts that are inert. The dust may also be composed of mixtures of the listed components. These powders or dusts do not substantially affect the stability of the foam that is added to the dry powder to produce the final foamed material. These dust materials are characterized by being easily incorporated into the foam to form the stable, fluid foamed mass. The fluid mass can be applied with little water and upon drying reverts to a dry, air dispersible powder necessary for the suppression of fire and explosion.
Further, any other additives that do not interfere with the fire prevention and suppression properties of the present invention may be added. These may include dispersants that facilitate the predampening or wetting-out of a dry dust material.
The density of the foamed dust material may generally be about 12 lb./cubic foot (192.2 kg/m3) to about 60 lb./cubic foot (961.1 kg/m3) but preferably is about 25 lb/cubic foot (400 kg/m3) to about 35 lb./cubic foot (560 kg/M3).
An advantage of applying the dust utilizing a foam carrier is that when the foam material is delivered such as by using a spray device, it allows the foam mass to adhere to the surfaces of the mine, enabling application of multiple layers until a desired thickness is achieved. Additionally, no excessive dust is produced during the application, thereby potentially eliminating the need to evacuate the mines during the process. The foamed material exhibits water contents of about 8% to about 40%, but preferably are about 10% to about 15% water by weight of applied material. The actual dust content is a function of the rate of addition of the pregenerated foam to the dust, the density of the pregenerated foam, and the dilution rate of the foaming agent prior to the generation of the foam. After application, the low water content of the material permits rapid evaporation of the water, resulting in a dry mass of fine, partly cohesive vesicular material that dusts readily.
The dust of limestone, dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings, and mixtures thereof, can be blended with the pregenerated foam at an underground station in the mine. To form the foamed material, the mixture is blended in a mobile tank. At the bottom of the tank can be a segmented auger screw that provides the mixing action needed to blend the foam with the dry powder. Preferably, a paddle mixer can be used that folds the pregenerated foam into the dry powder until the powder is blended with the foam as a homogeneous foamed material.
The mobile tank can be moved underground and positioned to any accessible area in the mine where the dusting activity may be required. Once at the position for application in the mine, a pump on or near the mobile tank is used to pump the foamed mixture through a hose and nozzle where it is applied to the walls and ceiling of the mine. Some of the foam structure is lost on impact with the wall. Because of the low water content of the foamed material, the loss of foam structure promotes rheological stiffening, making the mass sticky, and promoting adhesion to the surface and allowing build-up of the foamed material to a desired thickness. The velocity of the foamed material sprayed from the nozzle should not be so great as to destroy the foam structure of the applied foamed material entirely, but should allow the retention of a loose, fluffy foamed structure to retain the properties needed for the performance of the foamed material in the event of an explosion and mine fire.
In addition, if the foamed material is to be applied in more than one place, the material can be fabricated at a first location and pumped to stations within the mine. There, the material could be retained for use as needed without having to transport the material in large tanks for long distances throughout the mine.
As an example, but not a limitation, the foamed material can be applied by a continuous cavity pump, to pump the foamed material to a pneumatic application nozzle (such as a nozzle used for low velocity shotcrete and repair). The pneumatic application nozzle tends to break up the stream of foamed material as it enters the nozzle. The use of this nozzle allows adequate application of the foamed material onto the mine surface. The foamed material can additionally be applied using an xe2x80x9cairless systemxe2x80x9d. The simplest form of an airless system can be the elimination of the nozzle and reliance only on the pressure produced by a continuous cavity pump to apply the foamed material.
In one embodiment, the foamed material is adapted from a shotcrete process, for spraying the foamed material onto a mine surface. Although this specification describes shotcrete applications for illustrative purposes, the present invention is applicable to any application in which a foamed material is to be conveyed to an application point and sprayed on a mine surface.
In another embodiment of the present invention, a method is provided whereby pregenerated foam is added to the mixer and the mixer started. While the mixer is turning, the dust is added to the pregenerated foam and blended. More pregenerated foam is added to produce a cohesive foamed material comprising the dust of limestone, dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings, and mixtures thereof, that can be pumped.
In another embodiment, a dry powder formulation is used which contains the dust of limestone, dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings, and mixtures thereof; a trace amount of a dry powder foaming agent (preferably about 0.05% to about 0.5% by dry weight of powder formulation) and a trace amount of an additive (preferably about 0.25% to about 1.0% by dry weight of powder formulation) that reacts with the dust to produce a of gas upon contact with water. The dry powder formulation can be sprayed onto a wet surface (mine surfaces coated with water) or sprayed together with water to a mine surface. When the dry powder is mixed with the water, the dry powder formulation effervesces to produce a foamed material. As an example but not a limitation, any water-soluble additive that produces a mild acidic solution when added to water and reacts with the carbonates in the limestone or other dust material to produce the gas for foaming can be added to the dry powder formulation as a dust or dry powder. The resulting acid reacts, for example, with the calcium carbonate and magnesium carbonate of limestone dust to produce a gas that foams the mixture. Gas producing additives which can be used with the present invention include but are not limited to aluminum sulfate and monoammonium phosphate.
In a further embodiment, a dry powder formulation is used which contains the dust of limestone, dolomite, magnesite, Class F fly ash, silica fume, gypsum, anhydrite, non-expansive clays, fine ground mine tailings, and mixtures thereof; a trace amount of a dry powder foaming agent; and, a trace amount of an additive that reacts with the dust to produce a small amount of gas. In one embodiment, the foamed material containing the dust is generated in a mixer prior to application. In another embodiment, a specialized nozzle allows dry formulated powder material to be transmitted pneumatically to the nozzle, where an inline mixer blends water with the dry powder, thereby initiating effervescence, and sprays the resulting foamed material onto a surface. As an example, but not a limitation, of a specialized nozzle, a long shotcrete nozzle commercially available from Pump Haus, Dallas, Tex., could be used which would provide adequate mixing of the material with water and permit foaming of the dry powder formulation within the nozzle.
Additionally, the definition of xe2x80x9cdustxe2x80x9d should be given the meaning as one of ordinary skill in the field would understand it. More particularly, the definition of dust by WEBSTER""S NEW UNIVERSAL UNABRIDGED DICTIONARY, Simon and Schuster, incorporated herein by reference, is xe2x80x9cearth or any other matter so finely powdered and so dry that it is easily suspended in air; anything in the form of a fine powder.xe2x80x9d